1. Field of the Invention
The present invention relates to an information processing apparatus for information recording, reproduction and/or erasure by a recording medium loaded in the apparatus, and more particularly to such an apparatus for preventing the change or loss of information by monitoring the temperature of said recording medium.
2. Related Background Art
In recent years there have been active developments of optical information processing apparatus for high-density information recording or reproduction by irradiating an optical recording medium with a light beam. Among such optical recording media, there are already known, for example, so-called WORM (write-once-read-mostly) recording medium, capable of add-on only once, and an erasable recording medium utilizing a magnetooptical recording method or physical phase change. In the following there will be explained the method of information recording and reproduction, as an example, in case of a magnetooptical disk.
The magnetooptical disk is composed of a thin magnetic film formed on a substrate and having an easy direction of magnetization perpendicular to the plane of film, and records information by the change in the direction of magnetization of said thin magnetic film. During information recording, the magnetization of said thin magnetic film is aligned in advance in a direction, and said film is irradiated with a laser beam modulated digitally according to the information signal, under the application of a bias magnetic field of a direction opposite to the direction of said magnetization. Thus the area irradiated by the laser beam is heated close to the Curie temperature whereby the coercive force of said area is reduced, and said area is magnetized, by the influence of said bias magnetic field, in a direction opposite to the direction of magnetization of the surrounding area. Thus a magnetized pattern is formed according to the information. The information thus recorded can be optically read, by the well known magnetooptical effect, by irradiating the medium with a low-power unmodulated light beam. Said information can also be erased by applying a magnetic field of a direction opposite to that of the bias magnetic field at the information recording.
On the other hand, the above-mentioned recording media, particularly the magnetooptical recording medium, give rise to change or erasure of recorded information by a change in the materials themselves, if the medium exceeds a certain temperature. For this reason, the conventional apparatus are so designed to detect the temperature of the recording medium and to reduce the irradiating laser power if the detected temperature exceeds a certain value, thereby protecting the recorded information.
However, even in such conventional apparatus capable of monitoring the temperature of the medium, the recorded information may be changed or lost if the medium is merely placed in the apparatus in case the temperature increases further, even in the absence of the laser beam.